It is now widely accepted that insulin initially binds to cell surface receptors and this is followed by internalization and degradation of a portion of the bond insulin by a time, temperature, and energy dependent endocytotic process. While increasing information is being gained regarding the fate of internalized insulin, relatively little is known concerning the physiological fate of the insulin receptor itself. The overall goal of the proposed research in this application is to further elucidate the mechanisms by which insulin and its receptor are internalized and processed and to examine the biological significance of these processes as related to insulin action. In the proposed studies, photoaffinity labeling of the insulin receptor as well as other analytic procedures including affinity chromatography, electrophoresis, and autoradiography will be employed. The specific plans include: l) in situ photoaffinity labeling and characterization of the insulin receptors in intact viable cells using freshly isolated cells (rat adipocytes, hepatocytes) as well as cultured cells (IM-9 lymphocytes, human fibroblasts) as model systems, 2) studying the bioloical fate of the photoaffinity labeled insulin receptor in these cells under physiologic conditions, 3) studying the fate of photosensitive insulin in these cells without first prelabeling on the cell surface, and 4) examining if there is a relationship between insulin receptor internalization and processing and insulin's biologic actions in the target cells (adipocytes, hepatocytes and human fibroblasts). It is hoped that the results from these studies will provide new information regarding the mechanism(s) and pathway(s) of insulin-receptor internalization and processing and receptor regulation. Further knowledge in this area could have significant impact in our understanding of important pathophysiologic states such as obesity and non-insulin dependent (Type II) diabetes mellitus which are characterized by hyperinsulinemia, altered insulin receptor numbers and insulin resistance.